Several different kinds of door stops are available on the market. Typically, a doorstop is screwed into the baseboard of the wall, in the appropriate position such that when the door swings open, it strikes the doorstop rather than the wall. Without the use of a doorstop, the doorknob will chip the wall, and then dent, and probably eventually knock a hole through it.
Doorstops are certainly better than having a traditional doorknob impact the wall. However, they tend to be slightly unsightly, and to get in the way, and additionally are not particularly resilient. A typical doorstop has only a half inch or so of relatively hard rubber to absorb the impact of a door. Thus, if the door is repeatedly swung open and impacts the doorstop, it is hard on both the door and the baseboard on which the doorstop is mounted.
Because installation of the doorstop is almost always responsive to the doorknob impact problem, if the doorknob were made in such a way that there would be no damaging impact against the wall, there would be no need for a doorstop.
There is thus a need for a doorknob that is itself resilient, and will absorb the impact of striking against a wall, without damaging the wall, the door, or the doorknob.
In addition, currently bright colors are being used extensively in architecture and in interior decorating, not to mention clothing. Bright colors are in vogue. But traditional doorknobs are typically neutral, so that they will match, or at least not conflict with, the decor of any room.
It would be handy if a doorknob were available which could be changed in color or configuration or style by merely slipping the knob portion off of the relatively expensive remainder of the structure, and slipping on a doorknob of a different color or style.